The lumber business is increasingly competitive. Whether or not a sawmill can be operated profitably usually depends on maintaining high efficiencies. There is pressure on sawmill operators to make the most efficient use of every log processed as well as to maintain a high throughput. Modern sawmills are extensively automated. This is necessary because both logs and labour are major cost components in manufacturing lumber.
In sawmills it can be desirable to remove a board from the bottom of a stack of lumber. An example of this need occurs where a vertical arbor gang saw is used to cut a cant into boards.
Logs are typically made into rough green lumber by processes that include producing a cant by cutting boards or flitches from the outside of the logs. This is typically done after profile-scanning the log to determine the optimum planes along which the log should be cut to make the most efficient use of the wood in the log. The cant is then cut into boards by a vertical arbor gang saw. Depending upon the size of the log and the nature of boards that are desired, side boards may be cut from the cant before the cant is passed to the vertical arbor gang saw.
The top, bottom and side faces of a cant may not be completely planar. Wane can occur along the corners of the cant. Where this happens, one or more of the corners of the cant are not square along part or all of the length of the cant. The shape of the top and bottom of the cant, and therefore the shape of the top and bottom boards sawn by the vertical arbor gang saw are typically determined by the optimization process.
The vertical arbor gang saw cuts the cant into a stack of boards. The vertical arbor gang saw typically has multiple blades equally spaced-apart along a vertical arbor. The vertical arbor gang saw may have a plurality of arbors. The width of the gaps between the blades determines the thickness of boards cut from the cant. The bottom of the cant becomes the bottom surface of the bottom board. The top of the cant becomes the top surface of the top board. Where the corners of the cant have wane, one or both of the top and bottom boards may need to be re-edged to yield narrower boards having square edges. Re-edging is performed in a separate re-edging apparatus.
Stacks of lumber emerge from the vertical arbor gang saw at process speeds which may be approximately 500 feet/minute, or even faster. Top and bottom boards that need re-edging are typically sorted and separated from a stack of lumber manually. Manual sorting is time-consuming and expensive in terms of labour costs. Providing an area for manual sorting can take up space within a sawmill.
There exist devices capable of removing top boards from stacks of lumber. Such top board separators are not able to remove bottom boards.
There is a need for apparatus and methods for removing bottom boards from a stack of lumber. There is a particular need for such apparatus and methods that can remove the bottom board while the stack of lumber is moving downstream for further processing without interrupting movement of the stack of boards.